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Co-adsorption of cadmium(II) and glyphosate at the water–manganite (γ-MnOOH) interface
Umeå University, Faculty of Science and Technology, Chemistry.
Umeå University, Faculty of Science and Technology, Chemistry.
Umeå University, Faculty of Science and Technology, Chemistry.
Umeå University, Faculty of Science and Technology, Chemistry.
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2005 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 285, no 2, 493-501 p.Article in journal (Refereed) Published
Abstract [en]

The co-adsorption of Cd(II) and glyphosate (N-(phosphonomethyl)glycine, PMG) at the manganite (γ-MnOOH) surface has been studied in the pH range 6–10 at 25 °C and with 0.1 M Na(Cl) as ionic medium. Batch adsorption experiments, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS) spectroscopy were used for the quantitative analysis and the determination of the molecular structure of the surface complexes. The adsorption of Cd(II) and PMG in the ternary Cd(II)–PMG–manganite system was compared with the adsorption in the binary Cd(II)–manganite and PMG–manganite systems. The formation of three inner sphere surface complexes was observed, a ternary Cd(II)–PMG–manganite complex, a binary Cd(II)–manganite complex and a binary PMG–manganite complex. The surface concentration of the ternary complex and the Cd(II)–manganite complex was more or less constant throughout the pH range studied. However, the surface concentration of the binary PMG–manganite complex decreased with increasing pH. The major part of the binary PMG–surface complex was protonated. The ternary surface complex displayed a type B structure (Cd(II)–PMG–manganite). The average Cd–Mn distance obtained from EXAFS (3.26 Å) indicates that the binary and ternary Cd(II)–surface complexes are formed by edge-sharing of Mn and Cd octahedra on the (010) plane of the manganite crystals.

Place, publisher, year, edition, pages
2005. Vol. 285, no 2, 493-501 p.
Keyword [en]
N-(phosphonomethyl)glycine, Glyphosate, Manganite, γ-MnOOH, Cadmium, EXAFS, XPS, FTIR, Ternary surface complexes
Identifiers
URN: urn:nbn:se:umu:diva-2220DOI: doi:10.1016/j.jcis.2004.12.003OAI: oai:DiVA.org:umu-2220DiVA: diva2:140116
Available from: 2007-04-03 Created: 2007-04-03 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Modeling of glyphosate and metal-glyphosate speciation in solution and at solution-mineral interfaces
Open this publication in new window or tab >>Modeling of glyphosate and metal-glyphosate speciation in solution and at solution-mineral interfaces
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Glyphosate (N-(phosphonomethyl)glycine, PMG, H3L) is a widely used organophosphorous herbicide. It interacts with metal ions and mineral surfaces, which may affect its mobility, degradation and bioavailability in the environment. However, these interactions are far from fully understood. This thesis is a summary of five papers discussing the complexation of PMG with metal ions in aqueous solution and the adsorption of PMG and/or Cd(II) on different mineral surfaces.

The complexation of PMG with the metals Cd(II) or Al(III) in aqueous solution was investigated with macroscopic and molecular scale techniques. Potentiometric titration data were combined with EXAFS, ATR-FTIR and NMR spectroscopic data to generate solution equilibrium models. In the PMG-Cd(II) system, only mononuclear complexes were formed, while both mono and binuclear complexes were observed in the PMG-Al(III) system.

EXAFS, ATR-FTIR, and XPS measurements showed that PMG adsorbs to the surfaces of goethite (α-FeOOH), aged γ-alumina (γ-Al2O3) and manganite (γ-MnOOH) through one oxygen of its phosphonate group to singly-coordinated surface sites. Surface complexation models consistent with these spectroscopic results were fit to adsorption data using the 1pK reaction formalism. Electrostatic effects were accounted using either the Extended Constant Capacitance Model (ECCM) or the Basic Stern Model (BSM), and the charge of the surface complexes was distributed over the different planes. The formation of the surface complexes was described according to the following reactions:

≡MeOH(0.5-) + H3L <=> ≡MeHL(1.5-) + H2O + H+

≡MeOH(0.5-) + H3L <=> ≡MeL(2.5-) + H2O + 2H+

The coadsorption of PMG and Cd(II) on the surfaces of goethite and manganite results in the formation of ternary mineral-PMG-Cd(II) surface complexes, as suggested from EXAFS results. Previous EXAFS measurements have also established the coordination geometries for the binary goethite-Cd(II) and manganite-Cd(II) surface complexes. In addition to the surface reactions in the binary mineral-Cd(II) and mineral-PMG systems, a single ternary complex with the stoichiometry ≡MeLCd(OH)(1.5-) was sufficient to explain coadsorption data:

≡MeOH(0.5-) + H3L + Cd2+ <=> ≡MeLCd(OH)(1.5-) + 3H+

It was concluded that the affinity of PMG for the three mineral systems decreases within the series: goethite > aged γ-Al2O3 > manganite. The formation of the ternary surface complex is more significant on goethite surfaces than on manganite surfaces.

Place, publisher, year, edition, pages
Umeå: Kemi, 2007. 80 p.
Keyword
herbicide, glyphosate, surface complexation model, speciation, goethite, aged gamma-alumina, bayerite, manganite, cadmium(II), aluminium(III), potentiometric titration, adsorption
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-1074 (URN)978-91-7264-277-5 (ISBN)
Public defence
2007-04-27, KB3B1, KBC-huset, Umeå Universitet, 901 87 Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2007-04-03 Created: 2007-04-03 Last updated: 2009-11-18Bibliographically approved
2. Chemical Processes at the Water-Manganite (γ-MnOOH) Interface
Open this publication in new window or tab >>Chemical Processes at the Water-Manganite (γ-MnOOH) Interface
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Kemiska Processer vid gränsytan mellan vatten och manganit (γ-MnOOH)
Abstract [en]

The chemistry of mineral surfaces is of great importance in many different areas including natural processes occurring in oceans, rivers, lakes and soils. Manganese (hydr)oxides are one important group to these natural processes, and the thermodynamically most stable trivalent manganese (hydr)oxide, manganit (γ-MnOOH), is studied in this thesis.

This thesis summarises six papers in which the surface chemistry of synthetic manganite has been investigated with respect to surface acid-base properties, dissolution, and adsorption of Cd(II) and the herbicide N-(phosphonomethyl)glycine (glyphosate, PMG). In these papers, a wide range of analysis techniques were used, including X-ray photoelectron spectroscopy (XPS), extended X-ray absorption fine structure (EXAFS) spectroscopy, Fourier transform infra-red (FTIR) spectroscopy, atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), potentiometry, electrophoretic mobility measurements and wet chemical techniques, in order to obtain a more complete understanding of the different processes occurring at the manganite-water interface.

From the combined use of these techniques, a 1-pKa acid-base model was established that is valid at pH>6. The model includes a Na+ interaction with the surface:

=MnOH2+½ --> =MnOH-½ + H+ log β0 (intr.) = -8.20 = -pHiep

=MnOH2+½ + Na+ --> =MnOHNa+½ + H+ log β0 (intr.) = -9.64

At pH<6 the manganite crystals dissolve and disproportionate into pyrolusite (β-MnO2) and Mn(II)-ions in solution according to:

2 γ-MnOOH + 2H+ --> β-MnO2 + Mn2+ + 2H2O log K0 = 7.61 ± 0.10

The adsorption and co-adsorption of Cd(II) and glyphosate at the manganite surface was studied at pH>6. Cd(II) adsorption displays an adsorption edge at pH~8.5. Glyphosate adsorbs over the entire pH range, but the adsorption decreases with increasing pH. When the two substances are co-adsorbed, the adsorption of Cd(II) is increased at low pH but decreased at high pH. The adsorption of glyphosate is increased in the entire pH range in the presence of Cd(II). From XPS, FTIR and EXAFS it was found that glyphosate and Cd(II) form inner sphere complexes. The binary Cd(II)-surface complex is bonded by edge sharing of Mn and Cd octahedra on the (010) plane of manganite. Glyphosate forms inner-sphere complexes through an interaction between the phosphonate group and the manganite surface. The largest fraction of this binary glyphosate complex is protonated throughout the pH range. A ternary surface complex is also present, and its structure is explained as type B ternary surface complex (surface-glyphosate-Cd(II)). The chelating rings between the Cd(II) and glyphosate, found in aqueous complexes, are maintained at the surface, and the ternary complex is bound to the surface through the phosphonate group of the ligand.

Publisher
74 p.
Keyword
Inorganic chemistry, manganite, γ-MnOOH, mineral surface, acid-base properties, adsorption, Cd(II), N-(phosphonomethyl)glycine, glyphosate, PMG, surface complex, dissolution, disproportionation, XPS, EXAFS, infrared spectroscopy, SEM, AFM, potentiometry, electrophoresis, Oorganisk kemi
National Category
Inorganic Chemistry
Research subject
Inorganic Chemistry
Identifiers
urn:nbn:se:umu:diva-253 (URN)91-7305-634-0 (ISBN)
Public defence
2004-05-19, KB3B1, KBC, Umeå University, Umeå, 13:00 (English)
Opponent
Supervisors
Available from: 2004-04-29 Created: 2004-04-29 Last updated: 2009-12-04Bibliographically approved

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